1. Field of the Invention
The present invention relates to a document transport apparatus for transporting a document sheet to a predetermined processing position to read the document sheet, and more particularly, to a document transport mechanism for reversing the side of a document sheet of which one side is read again to a read position to read both side of the document sheet, and collating document sheets of which both sides are read to discharge.
In recent years, for a document transport apparatus mounted on an image reading apparatus, various path configurations and document feeding procedures have been proposed to reduce the reading time in reading both sides of document sheets.
2. Description of the Related Art
In recent years, for a document transport apparatus mounted on an image reading apparatuses, various path configurations and document feeding procedures have been proposed to reduce the reading time in reading both sides of document sheets. As one of the document transport apparatus, a plurality of switchback paths is provided on the downstream side of contact glass having a read position to read the document sheets.
In this type of apparatus, there is an apparatus in which a first document sheet of which the front side is read in a read position is switched back in a first switchback path, a second document sheet is switched back in a second switchback path, the switched-back document sheet is fed again to the read position to read the back side, and the document sheet of which both sides are read is switched back in a switchback path for discharge, then reversed, and discharged from a discharge path that is also used as the second switchback path (for example, Japanese Patent Application Publication No. 2005-289565).
Further, another apparatus has been known where a document sheet of which the front side is read in a read position is switched back in a switchback path for re-feeding, then reversed, and fed again to the read position to read the back side, and the document sheet of which both sides are read is switched back in a switchback path for discharge, and is discharged from the discharge path used also as the switchback path for re-feeding (for example, Japanese Patent Application Publication No. 2006-327728).
Then, in these apparatuses, reading efficiency of two-sided document sheets is improved by controlling transport so as to transport the front side of a first document sheet, the front side of a second document sheet, the back side of the first document sheet, the baCk side of the second document sheet, the front side of a third document sheet, the front side of a fourth document sheet, the back side of the third document sheet, the back side of the fourth document sheet, . . . to the read position in this order in reading the two-sided document sheets.
However, since the former apparatus is comprised of the first, second and discharge switchback paths, the configuration is complicated, and the apparatus becomes large. Further, in the second switchback path also used as the discharge path, unless the second document sheet to be switched back is carried out of the path, the first document sheet cannot be discharged. In the discharge switchback path, unless the first document sheet is discharged, the second document sheet cannot be carried in the path.
In the latter apparatus, in each of the switchback path for re-feeding and the discharge switchback path, unless a first document sheet is carried out of the path, a second document sheet cannot be carried in the path. Further, in the switchback path for re-feeding, since this path is also used as the discharge path, unless the second document sheet is discharged, a third document sheet cannot be carried in the path. Furthermore, for large-size document sheets, transport is controlled so as to read the front side of a first sheet, the back side of the first sheet, the front side of a second sheet, the back side of the second sheet, . . . , and therefore, the processing time significantly increases in reading the large-size document sheets.
In other words, there are problems that the apparatus becomes complicated and large in the former apparatus, and that the processing time significantly increases in reading large-size document sheets in the latter apparatus. Further, in both of the former and latter apparatuses, the configuration and transport operation of document sheets is controlled so that an only single document sheet exits in each of a plurality of switchback paths, and there are limitations in further reducing the reading processing time of document sheets and improving productivity.
It is an object of the invention to provide a document transport apparatus for further reducing the processing time to read both sides of document sheets, and improving productivity in two-sided document sheets.